1. Field of the Invention
The present invention is related to an arrangement for suppressing an interfering component in an input signal, said arrangement comprises means for deriving an estimate of the interfering component, subtraction means for determining a difference signal from the input signal and the estimate of the interfering component.
The present invention is also related to a loudspeaking telephone.
2. Description of the Related Art
An arrangement according to the preamble is known from U.S. Pat. No. 5,390,250.
This arrangement has widespread applications such as acoustic echo cancellers and noise cancellers. In these application there is an input signal in which an interfering component is present.
This interfering component can e.g. be a signal received from the far end in a loudspeaking telephone system. This far end signal is reproduced by a loudspeaker and is received by a microphone together with the near end signal e.g. from a local speaker. The input signal is now a signal derived from the output signal of the microphone. Because amplifiers are included in the transmit path, the loop gain for a specific frequency may be greater than 1, resulting in oscillations. If the acoustic feedback is smaller than 1, oscillation will not occur, but after a certain delay an echo of the signal applied to the input of the send path will appear at the output of the receive path via the far-end echo path. In telephony this means that a speaker hears his own voice delayed by a specific period of time. This phenomenon is experienced as extremely annoying especially in case of long delays.
To prevent this undesired feedback, in an acoustic echo canceller a replica of the undesired component is derived from the far end signal by means of an adaptive filter. Said replica is subtracted from the input signal, in order to eliminate the undesired component signal.
In case of a noise cancelling system the undesired component is a noise signal coming from a noise source, e.g. the noise of a running engine in a car. To eliminate the noise signal, a replica of the noise signal is derived from a reference noise signal received from a reference transducer by means of an adaptive filter. Again, this replica is subtracted from the input signal.
A problem with adaptive filters is the limited ability to track fast changes of the transfer function to be reproduced. Such a fast change can occur due to the movement of a person in the room in which the echo canceller or noise canceller is used. This can result into a reduced amount of suppression of the undesired component, a problem that is not satisfactorily solved up to now.